In two recently issued United States Patents covering inventions of which I am a coinventor, namely U.S. Pat. Nos. 4,011,119 and 4,070,852, a detailed discussion of the problems associated with lidding of disposable cups is provided. Means is disclosed therein for providing a cup closure which is, in at least some respects, functionally superior to conventional preformed plastic lids. This is achieved by cold vacuum stretching a web of elastomeric film over a cup, and thereafter releasing the web to allow the inherent restorative properties of the film to cause it to contract about the periphery of the cup, and to actively conform thereto, thereby forming a seal which is maintained, notwithstanding the deformation that occurs in normal use.
While highly effective and facile to use in the manner described therein, the apparatus taught in the foregoing patents is rather complicated and costly. Accordingly, it was desirable to develop a simpler, less expensive, and more portable device which would be capable of achieving substantially the same result.
A recently issued United States Patent to Balzer et al, U.S. Pat. No. 4,078,360, describes an apparatus for sealing a film onto the top of a cup by application of heat and direct contact between the heating apparatus and the film. This patent relies on the heat seal rather than the elastomeric restorative forces disclosed in this application, and hence entails evident disadvantages.
Muller teaches, in U.S. Pat. No. 2,218,293, method and apparatus for wrapping an article in cellophane, which require the cellophane to be first emplaced against the article, then wiped along its sides as the article is passed through the wrapping device. There is no mention of a method or device for substantially stretching a film for emplacement on a cup or similar article, and the device disclosed would not function in that manner.
In U.S. Pat. No. 3,849,972, Pepmeier teaches apparatus for applying to a cup a film lid, which film (e.g., of polyvinyl chloride) has a tendency to cling to itself, or to parts of the cup or to the apparatus. The cup is urged against the individual film and through an opening surrounded by resilient members, which externally press the film against the side of the cup, and fold it against itself. There is no mention of stretching the film. Nor is there any provision for holding the film against disengagement from the device during application of the film lid.
Finally, in U.S. Pat. No. 3,851,440, Horsky teaches an apparatus for wrapping lettuce, the use of which includes the step of passing the already wrapped product through a perforated disk having flexible fingers, which fingers serve to sweep the excess film over the wrapped lettuce to thereby form an overlying envelope. While Horsky employs a disk which appears similar to one of the components of applicant's device, there is no teaching which would lead to applicant's invention. Further, the combination of that disk with any combination of the other components of Horsky's disclosure does not provide a device adaptable either to function in the same manner or to provide the same wrapped product as applicant's invention.
It is therefore an object of this invention to provide a novel device for mechanically stretching an elastomeric film and applying it as a closure to a cup or the like, which device is simple, inexpensive and highly portable.
It is also an object of the invention to provide a novel method for so stretching and applying an elastomeric film, which method is facile and effective.